Pressure Drop Research On Air Flowing Across Falling-film Horizontal Tube Bundle And Circular Finned Tube Bundle

An experimental platform for air flowing across falling-film horizontal tube bundle has been set up to investigate flow resistance characteristics of in-line falling-film tube bundle and staggered falling-film tube bundle.A series of experiments have been carried out to investigate how the pressure drop was affected by different operation parameters(spraying density,air velocity)and different structural parameters(transversal pitch,longitudinal pitch,external diameter of tube and the number of tube rows).The results reveal that spraying density showed small effect on pressure drop.When spraying density increased from 0.015 to 0.035 kg/(m?s),the pressure drop of staggered falling-film tube bundle increased about 12.3%,and the pressure drop of in-line falling-film tube bundle just increased about 8%.When the inlet velocity of air is faster than 3.2 m/s,the water film is found to blow off from staggered tubes,which greatly increased experimental pressure drop.However,this pressure increasing phenomenon has not been observed on the in-line falling-film tubes.Compared with longitudinal pitch,transversal pitch has significant impacts on pressure drop.When transversal pitch diameter ratio decreased 0.3,the pressure drop of staggered falling-film tube bundle increased about 34%,and the pressure drop of in-line falling-film tube bundle increased about 38%.When other structural parameters are fixed,the pressure drop of staggered falling-film tube bundle increases linearly as the number of tube rows greater than 4,while the pressure drop of in-line falling-film tube bundle increases linearly as the number of tube rows greater than 2.Meanwhile,pressure drop correlations,of which fitting error is less than ±20%,for air flowing across horizontal staggered falling-film tube bundle and in-line falling-film tube bundle has been respectively proposed.In addition,flow resistance characteristics of air flowing across circular finned tube bundle have also been investigated by numerical simulation and experiment.The structural parameters including transversal pitch,longitudinal pitch,external diameter of tube and the number of tube rows have been studied.Three-dimensional numerical models of the circular finned tube bundle with different structural parameters have been built respectively to predict the pressure drop under different air flow rates.By considering the fin-tube bundle as porous media,the viscous resistance coefficient and inertial resistance coefficient of each model have been obtained by the flow resistance equation of porous media.The results indicat that compared with longitudinal pitch,transversal pitch and tube diameter have significant impacts on both the viscous resistance and the inertial resistance.By associating the viscous resistance coefficient and the inertial resistance coefficient with structural parameters,correlations of pressure drop about the circular finned tube bundle have been established.The fitted values are in good agreement with experimental values.Furthermore,the pressure drop of staggered circular finned tube bundle increases linearly as the number of tube rows greater than 4 when other structural parameters are fixed.Pressure drop correlation for air flowing across circular finned tube bundle has been proposed,of which fitting error is less than ±20%.